Role of VE-cadherin cleavage as a clinical marker and trigger of endothelial barrier breakdown in sepsis

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Recently Sepsis was defined as a life-threatening organ dysfunction due to a dysregulated host response to infection. A key event preceding organ dysfunction in sepsis is loss of microvascular endothelial barrier function. The integrity of the endothelial barrier is dependent on intact adherens junction protein vascular endothelial cadherin (VE-cadherin). Previously, we have demonstrated that VE-cadherin is cleaved in response to inflammatory stimuli leading to the generation of sVE-cadherin which consists of the extracellular domains EC1-5. Formation of sVE-cadherin was shown to occur in strong correlation with loss of endothelial barrier function in vitro and was significantly augmented in patients microvascular barrier dysfunction in severe sepsis. Our preliminary data show that recombinant sVE-cadherin is not only the result of inflammation but rather is dose-dependent inducer of endothelial barrier dysfunction independent of apoptosis. Therefore, the aims of this proposal are to characterize the mechanisms underlying sVE-cadherin formation as a result of inflammation and to identify the role of sVE-cadherin-induced loss of endothelial barrier dysfunction in vitro and in vivo.Based on our preliminary work we will elucidate the cellular mechanisms contributing to the formation of sVE-cadherin in detail by investigating how the sheddase ADAM10 which is responsible for sVE-cadherin generation is regulated in endothelial cells. Since sVE-cadherin dose-dependently induces loss of endothelial barrier function we will identify the underlying mechanisms. Using atomic force microscopy we will test whether sVE-cadherin blocks VE-cadherin-mediated adhesion. In immunoprecipitation we have identified a direct interaction of sVE-cadherin with barrier-regulating phosphatase (VE-PTP). Therefore, we will test whether sVE-cadherin via binding to VE-PTP leads to altered phosphorylation of VE-cadherin or modulates Tie-2-dependent signaling pathways independent of inflammatory stimuli leading to loss of endothelial barrier function. In our in vivo sepsis models we will investigate the time course of sVE-cadherin formation and its direct correlation with inflammation-induced microvascular barrier dysfunction. Furthermore we will test whether application of sVE-cadherin to healthy animals induces loss of microvascular barrier function and organ dysfunction comparable to their occurrence in sepsis. Taken together these experiments will identify a novel pathophysiologic aspect in the complex context of sepsis-induced microvascular barrier dysfunction.